1. Field of the Invention
This invention relates to a method for dispensing a defined minimum quantity of a liquid or pourable substance into a container, in the process of which the amount of the substance dispensed is measured and a valve closes to terminate the filling process as soon as the amount delivered has reached a specific final value.
In the production and distribution of liquid or pourable substances such as beverages, the filling of these substances into containers, for instance bottles, plays a significant economic role. Typically, the substance is dispensed by a large filling and packaging system such as a rotary bottling machine, for instance with 150 bottling stations that permit the simultaneous filling of 150 bottles. A rotary bottling system of that type is capable of filling up to 70,000 bottles per hour, each holding one liter of the beverage concerned. Overfilling each bottle with only 5 milliliters of beverage adds up to an error amount of 350 L per hour, 850 L per day and about 250,000 L per month. Hence, for cost reasons alone, accurately quantized dispensing of the beverage is highly desirable.
2. Background Information
In prior-art packaging systems, the filling of the containers with the substance concerned typically involves the following steps. The substance is delivered from a storage tank through a valve into a container, with the quantity of the substance delivered to the container, typically its volume or weight, being measured by means of a mass or volume flowmeter. As soon as the dispensed amount of the substance thus measured has reached a setpoint value, hereinafter referred to as the final value, the valve closes, terminating the filling process.
The closing of the valve, however, takes a finite length of time as a result of which, after the predefined setpoint value is reached, an additional amount of the substance is delivered into the container, a phenomenon referred to as tailing. Such tailing is also attributable to the fact that the valve, being a mechanical component, and the valve-controlling device activating the valve, are subject to response and dead times. As a rule, then, the amount of substance dispensed into the container exceeds the final value at which the closing of the valve is to terminate the filling process.
In prior-art packaging methodology, this problem is often addressed by measuring for each container filling the tailing amount and comparing it with the minimum amount that should be dispensed into the container. The difference between the measured actual amount and the setpoint minimum amount, constituting the tailing, is deducted from the nominal quantity in subsequent filling processes either in stepwise fashion, i.e. only by a certain percentage at a time, or by establishing a floating mean value from the tailing values of several consecutive measurements. The actual amount dispensed into the container concerned is thus reduced, approaching the targeted minimum amount over the course of several consecutive filling cycles. An immediate, complete adjustment in the second filling cycle for the tailing measured in the first cycle is not possible, given that such compensation would be subject to unstable fluctuation.
It is in particular at the time of the startup of a filling system, for instance on changeover to a new substance, or after cleaning or after being reset for a different container capacity, that the initial quantities dispensed are quite inaccurate, so that the amounts filled into the containers often exceed established tolerances. Taking for instance a large rotary bottling system with 150 bottling stations, any startup of the system can result in as many as 1,000 improperly filled and thus partly unsaleable bottles.